The use of RFID (Radio Frequency Identification) technology is very common in the modern day world. One specific such use is in door lock mechanisms (such as for individual hotel rooms), in which case the door lock may include an RFID reader to detect the proximity of a device worn or held by a hotel guest and unlock the door. Problems with unlocking doors can occur due to challenging ergonomics related to door jams and door handles, due to the short read range of the RFID reader, and/or due to less than optimal performance by the RFID reader. It is desirable to increase the success rate of unlocking doors when hotel guests have their device within a reasonable proximity of the door lock mechanism.
Many forms of RFID make use of electromagnetic induction between a pair of coils (loop antennas), one typically located in an RFID reader and one typically located in an RFID tag. One class of RFID technology is known as Near Field Communication (NFC) in which a pair of devices establish radio communication when they are brought to within a certain minimum distance of each other (e.g., 10 cm or less). NFC devices may typically operate at an RF frequency of 13.56 MHz. Other RFID frequencies may be in the range of 125 kHz, 433 MHz, 866.5 MHz, 915 MHz, and in the microwave frequencies, to name a few.
One parameter of an antenna and associated circuit is known as a quality-factor (or Q-factor). It is a dimensionless quantity that describes how under-damped an oscillator or resonator is, in addition to characterizing a resonator's bandwidth relative to its center frequency. Higher Q indicates a lower rate of energy loss relative to the stored energy of the resonator; the oscillations die out more slowly. A pendulum suspended from a high-quality bearing, oscillating in air, has a high Q, while a pendulum immersed in oil has a low one. Resonators with high quality factors have low damping so that they ring longer. With antennas and their associated circuits, a high Q-factor means the antenna and circuit will resonate longer than if they had a lower Q-factor.
It is against this background that the techniques described herein have been developed.